1. Field of the Invention
The present invention is directed to a system which extracts, from uncoded video data, coding parameters relating to a previous coding process. The invention has particular utility in multi-generational coding systems, in which the same video data is coded and decoded a plurality of times.
2. Description of the Related Art
Generally speaking, a multi-generational coding system includes encoder/decoder pairs arranged in series relative to transmission media. In operation, each of the encoders is adapted to code uncoded video data and then to transmit that uncoded video data over a transmission medium to a decoder which is adapted to decode the coded video data. These systems are in wide use today, particularly where frequent transmission of video data from one location to another is required, such as in the television industry.
Problems arise in multi-generational coding systems of the foregoing type due to the way in which encoders in these systems code video data. More specifically, in these systems, different encoders code the same video data by recalculating coding parameters for each coding operation. Differences in coding parameters resulting from these calculations cause quantization noise to be introduced into the video data. Eventually, following several generations of coding, sufficient quantization noise is introduced into the video data to cause a marked degradation in video image quality.
One conventional solution to the foregoing problem involves introducing additional data, termed a "mole", into decoded video data. This additional data defines coding parameters to be used for the video data, and is transmitted, along with the video data, between encoders and decoders. Use of a mole, however, has several drawbacks. First, the mole must be invisible, otherwise it would affect the quality of images produced from the video data. Making sure that the mole is invisible can be difficult from a technical standpoint. Second, special hardware may be required to transmit video data having a mole, otherwise the mole may be altered during signal transmission. Finally, hardware modifications may be required to ensure that decoders are capable of detecting the mole and of separating the mole from the video data. For at least these reasons, the mole, and systems like it, have proven an inadequate solution to the above problem associated with multi-generational coding.
Thus, there exists a need for a system which reduces the amount of quantization noise introduced into video data during multiple coding processes, without introducing additional information into the video data itself.